Stop Saying Car Exhausts Need Back Pressure
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- Опубліковано 4 чер 2024
- Why Car Engines Don't Need Back Pressure + Exhaust Scavenging
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Do cars need back pressure? How should you size an exhaust? What exhaust diameter is too large, or too small? What is exhaust scavenging? What is wave scavenging? Why is exhaust velocity important?
Cars don't need back pressure. More specifically, internal combustion engines do not benefit from back pressure in the exhaust. Back pressure is a pressure in the opposite direction to the exhaust's flow. The goal of an exhaust is remove spent combustion gases as quickly and efficiently as possible out of the engine cylinders. Back pressure has the opposite effect, impeding exhaust flow.
Exhaust velocity, and exhaust scavenging, however, are highly beneficial. This video will discuss wave scavenging, inertial scavenging, and how exhaust pipe length and diameter play a critical role in exhaust velocity and scavenging effectiveness.
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NEW VIDEO EVERY WEDNESDAY! - Авто та транспорт
I stopped doing absolutely nothing to watch this, it better be good
Hahaha, I'll do my best to entertain you for the next 9 minutes. :)
Engineering Explained update: it was good
Ryan Aponte Hey I just saw that you left this exact comment on ss717's vid :)
Supercharged Mustang GT yes I did :)
it was good. I learned that I missed my chance a few months ago to see a HP increase by driving around when the eye of Hurricane Irma passed by, due to lowered atmospheric pressure.
Oh yeah, I get it!
*Mounts 10" straight pipe into his '90 Honda*
Praise be.
now I want to know how to calculate length/diameter for my project honda.... :/
How much you paid for it on craigslist (a)
Amount of monster stickers on the car (c)
Desired ricer factor (1-10) (b)
a / c + b = diameter in mm
StanceArmy Jimmy same here
Yeah because s2ks are from the 90s 🙄
As an engineer I’ve always been irritated by people saying cars need back pressure.
Drove me nuts
Isn't it necessary to help boost mpg?
The guy who did my muffler delete on I4 said these engines need a bit of back pressure. I definitely felt a loss of torque at lower rpm. Also I’m surprised that so many mechanics think no tuning is needed after a muffler delete. My area doesn’t have that so yeah car sounds nice and loud with lesser torque which means loss in performance. ☹️
I do have a k tuner. Do you know if I can tune muffler delete by myself? And if so how?
@Engineering Explained
@@Febreeze_Odor_Eliminator you believe that coming from a guy who chops mufflers off for a living?
The only reason you “need” back pressure, is because it was tuned for it, from factory.
So of course it “needs” it, but engines are just air pumps, why have a higher differential in pressure, when could just NOT
@@rocketkinger2506 so if I straight pipe my 4 wheeler, I just need to rejet it and it's good? After I upgrade the intake
@@rocketkinger2506 That's a lie
So I dont need anything after my headers. Gotcha
Who needs headers? I use those save the turtles metal straws instead, cheaper that way
@@Snow-vo1yi gives you that perfect exhaust note too 👌
Unequal length straws
@@Snow-vo1yi Headers are just really big metal straws
I would love to have side pipes for each cylinder out of the fenders.
me: gets pulled over
cop: your vroom too loud!
me: "my vehicle is operating at maximum efficiency, and reducing pollutants while increasing performance. *shows cop video*
cop: understandable, have a nice day
Ya mate, that's not going to happen. Play this youtube video for the cop, you may go to jail.
@@netprowlerp you must be so much fun at parties, I bet you're idea of "rebellious" is missionary with the lights off.
@@ljgarrison6910 😂😂😂😂
@@ljgarrison6910 Hahaha. have to tell that to my wife. She would beg to differ.. Ya, not everyone here is 12 years old.
@@netprowlerp he was making a joke. And you took it too seriously finally calling his audience 12 year olds without knowing the real ages. The only thing you should be telling your wife is organizing counseling cause you're way to serious.
One of the biggest arguments among builders & tuners ever. thanks E.E. for breaking it down!
+TheGhost ....lol, you're absolutely right!
More like among wannabe tuners and builders.
+Mathieu Levasseur .....lol, also true
wish this video was available before i wasted so much time explaining this fairly simple concept to people. could have just dropped the link and walked away lol
engine masters on the motortrend channel did dyno tests with different full exhaust systems and pretty much theres no such thing as too big of exhaust but you do lose a some power and torque at the very start like below 2.5k rpm. what people don't really look at though is partial throttle tuning and just going bigger everywhere can hurt that response and drive-ability.
Thank you I'm so tired of people saying ”back pressure " !
back pressure.🤭🤭🤭🤭🤭
Whatever you want to call it, if you have no back pressure at all, it sounds like ass. You need some kind of baffling and resonance to tune the sound and make it sound good.
@@80s_Boombox_Collector so engines don't get damaged with free flow exhausts? Dragracers rebuild after every race so yeah
Them rebuilding has nothing to do with “back pressure “ or lack there of. Correlation =\= causation.
@@tejaspadhye I thought the lacl of tread on the tires caused them to need to rebuild
It's amazing that people will not listen to a word you said because Cleetus at Smithys Muffler Shop tells them the backpressure of a Flowmaster will give them more power
Interesting comment. I think it was in the first minute or two of the video that the feller explains why some back pressure is good.
@@CalebDiT Did you watch the same video?
@@CalebDiT No, he mentioned it and shrugged it off as if it was to complicated for us poor folk to understand. He never explained it. Also the title of the video is "Back Pressure is Bad!".
@@CalebDiT What he said was having a balance of velocity and restriction is ideal, not that having some back pressure is good. More restriction increases exhaust velocity but inhibits overall flow of exhaust, less restriction allows more exhaust flow but lowers velocity.
@@Talos_Valcoran87 You and the video maker seem to understand what is necessary, but you don't like the terms. "Back pressure is bad, but some calculated restriction is ideal." It's a contradiction to anybody truly listening.
the best thing to do in the last hours of 2017: watching Jason's explanation with his whiteboard. Nice as always, man!
thanks for the love Jason!
5 4 3 2 1 happy white board!
That is what I am doing, I even wonder if I will be going to celebrate at my cousin's in an hour or 2:)
Or last 60 minutes of 2017..!
No Roadkill #72....It didn't come out on time. So end the new year learning valuable stuff instead of watching Junk Food.
Engineering Explained coming in clutch with the last vid of 2017
Happy New Year!!
And a happy new year to you too bro!
First of 2018 here😂
no one says clutch
Squidwards crib does buster
some Guy: you´re losing power, you need back pressure.
Me: (inserts banana in tailpipe)
Guys, I keep blowing engines. What happened. I listened to a guy on youtube. Do you have bananas for brains?
Lmfao
*losing
MCM put a potato in the exhaust of an old Corolla and it actually made more power.
"Yeah, we're not gonna fall for a banana in the tailpipe."
He seems almost agitated making this one ill bet somebody ticked him off
And I understand his frustration so well.
The argument of what back pressure is, is an argument as old as hot rodding.
*some guy at the auto part store says something about back pressure*
EE: races home and starts writing furiously on a whiteboard while collecting valid explanations.
I get aggravated when most people open their mouth, I cannot believe he is as cool headed as he is!
I think he knows his team have let him down, some of the stuff at the beginning of the video is very messy, not false, but over simplified and a a result not accurate.
Back pressure is not air trying push back into the exhaust (and I think he knows this), it's the positive pressure built up by exhaust gases inside the exhaust system, the higher the engine rpm, the higher this pressure, which is why some high performance vehicles switch between 1 or 2 exhaust backboxes at specific rpms to alter the "back pressure" in the system to maintain higher performance and fuel economy throughout the rev range.
Can't tell you how many old guys I have argued with about this. I quit years ago. Velocity they confuse it with back pressure. Yeah smaller pipes have high low rpm velocity, so you get better low rpm scavenging and better low end power. But then at some point they start choking the engine.
Mean Man You're incorrect
Kevin Norris ... said the old guy.😜
I thought the high and low end power came from the length of the header/manifold tubes?
i had a 150cc scooter, and the studs that hold the exhaust to the exhaust port broke one time, and made the scooter so slow, it was normally able to go 60ish mph, and with the open exhaust port, it could barely go 15mph
Devin Royce was it 2 stroke?
Thank you, thank you, thank you! I'm glad you made this. Please, make sure this goes on Wiki-everything! _My man_
Nice work!!! And you are absolutely right, this is GOLD for all amateur tuners!
My advise to budget track cars; Keep stock exhaust diameter, remove cat, get "straight through" resonator and muffler (with a tail/end dia' similar to exhaust dia' = no deep tone, pure race sound), this will roughly give you same performance boost as a expensive $1500, from headers and back, race exhaust
@EE:
if you don't take into account the Euro and newly establish similar US emission restrictions (completely disregarding the cat here) the backpressure is needed to recirculate some of the exhaust back into the intake, to burn unburned fuel, at given loads at specific rpms. So in modern cars it's needed to fulfill legal requirements ;) PS not all engines need this system, but if you increase 1st weight in your search terms and 2nd search increase engine volume/capacity and cross those you'll find it being implicated more and more
YES!! Thank god! So sick of hearing the crap about "needing" back pressure.
Yep. Beat me to it.
you cant have scavenging without backpressure. you don't need it... drag cars don't have scavenging. lmao
You DO need at least some back pressure to get good sound. Try taking off everything after the headers. It will sound like ass.
@@80s_Boombox_Collector Sound doesn't help it go, contrary to what every Honda driver around here seems to believe.
@@Jupiter__001_ No, but good sound makes it more enjoyable.
Thank you Jason for your great videos - I graduated in 1977 then went post-grad but I am still learning, your delivery style is enlightening and your enthusiasm teaching is contagious. You may mention the component to the scavenging negative (relative) pressure wave contribution from other cylinders connected to the same collector, what we used in "tuned header exhaust".
As I read comments, I think that some people misunderstand the "negative" pressure wave (or interface) you are mentioning possibly because they consider the word "pressure" as necessarily positive not considering that this "pressure wave" is negative relative to the pressure in the rest of the system. Great video - makes me feel young again.
PS: Born in '53! What is your secret, are you wearing a wig, genetics, special engine oil formulation, ;-), take care Ciao, L (FoMoCo engineering retired)
Hey Jason.👋 While some have mentioned the whiteboard looks a bit small and restrictive at times, my guess is that it has been engineered to just the right size for this application.👌 Much like your explanation in this video, everything on the board usually has a good, positive flow without feeling restrictive. We all know, knowledge is power and the power to weight ratio of the whiteboard is immense!💪 Great flow and power without undesirable drone... what more could we ask for? Thanks for a fantastic run in 2017 and all the best to you in 2018, sir. ✌😉
Ha, thanks for the fun comment, happy new year!
Should get an award for most efficient UA-cam creator.
If you ever want to do a charity fund-raiser, take the current whiteboard that's been used in so many EE episodes, sign it in permanent marker, and stick it on ebay.
Good comment but get rid of the freaking emojis lol
gooz0mbie Thanks, but that's what happens when you give old people "smart" phones... Dad jokes and emojis.😜
You have absolutely no idea how helpful your videos are. I just recently started trying to learn about my car and attempt to fix it myself. I normally troubleshoot radar equipment but when it came to my car, I was lost. No one could explain the theory to me very well so I found it very difficult to troubleshoot the symptoms I had. Your videos changed everything. Thank you.
Happy to hear it, thanks for watching!
Yea he's spot on, think of your exhaust and intake for that matter like sucking a milkshake through a small diameter or larger diameter straw. Or sticking your thumb over the end of a garden hose.
I thought you owned a toy company? You changed to radar equipment after the war?
A video idea would be how to go about tuning an exhaust system to a specific engine and the tools and experience required to do so!
Thanks once again Jason, your videos are so simple but explain such complex interaction principles that the usual layman fails to understand.
As a side effect, you just explained why a 2 stroke engine produces so much power/torque at a very narrow rev band (power band).
But you need some back pressure (and the back pressure wave) to stop all (most) of the exhaust gasses escaping at the critical moment down the exhaust pipe (must be tuned).
You are dealing with principles of physics, where - due to exhaust gas inertia, scavenging, back pressure wave and hitting the sweet spot in the revs to achieve the optimum efficiency to get max power out, while not sacrificing some of the unburned - fuel-air mix vapour out the exhaust too.
And that is what Tuning is all about, whether you are optimising for power, fuel efficiency or to keep the temperature of the exhaust the lowest!
I live in the heart of NASCAR country, and the old time engine builders would bolt a straight pipe on the headers and run the engine up to 7k rpm, and where the pipe glowed cherry red, he'd cut the pipe and weld on a turn out. Said that little trick would add 5hp... This was back in the early 80's, so don't take any of this for gospel ;-) Excellent explanation Mr EE :-)
Painting flames on it adds another 5 hp.
That is exactly what they did- old drag racers know this.
I will explain to you the source of the backpressure myth. In the late 1970's carbureted cars were forced to run an extremely lean mixture. The older catalytic converters were quite restrictive. These cars were able to run so lean (without melting pistons) because the old catalytic converters created a form of passive EGR. If the exhaust on these cars is replaced with a less restrictive system the passive EGR was no longer present. These cars would run VERY lean, melt pistons and overheat UNLESS the carbs were replaced with pre-emissions carbs.Timing was not computer controlled and knock sensors did not exist. Hot engine, lean mixture, detonation... BOOM!
It was a crappy system, there were 350 cu. in. V8's with less than 150 hp! So many vacuum hoses were required that underhood vacuum maps were quite detailed. Bad days for automotive tech.
So basically, early emissions systems were crappy and complicated, and were doomed to kill power unless there was an electronic babysitter to reign everything in efficiently? Big shocker.......
The 70's???? You've got to be kidding me. Or is that as far back as you remember? Because exhaust tech as you explained goes way back beyond the 70's vehicles.
D.E.B. B what he's saying is it really originated in the emissions days, which started very late 60s and came full swing in the 70s, that's when it really became an issue and the backpressure idea came to light
D.E.B. B - Catalytic converters became mandatory in the early 1970's. The tech was not the same in the 1960's. My first car was a 1967 Camaro one owner, low miles PERFECT...$1200; it was very simple (points, carb, drum brakes (all of them), and it had about 3 vacuum lines under the hood). My second car was a 1975 Monte Carlo. The Monte Carlo had dozens of vacuum lines, a cat, front discs, HEI ignition, AND IT WAS SLOW AS MUD. *Car tech changed drastically between 67 and 75.*
Catalytic converters did not become mandatory, it only seemed that way. Exhaust emission limit levels kept being reduced, and because of that, MOST auto manufacturers began using a catalytic converter in 1975 because they couldn't figure out any other way to meet the emission standards. That was the beginning of no lead gas,because the lead would supposedly coat the tiny platinum catalyst pellets inside the converter (I don't remember ANY cars using a cat con before 1975, and then all of a sudden, it seemed like all of them did). However Honda's CVCC engine (in Civics and Accords) was able to meet the emission standards WITHOUT a catalytic converter all the way until 1980 (except in California, I think that Honda needed cat cons there in '78). Exhaust tech did not change; as he mentioned in the article above, was just part of the science involved to get the engines to make certain amounts of power at selected points in the torque curve, while keeping the noise to a minimum. Short open pipes were usually used on vehicles that needed to make maximum power at high rpm's. Longer, smaller, more restrictive exhausts were used on street vehicles that had to be quiet. Somewhere in the middle were exhausts which were a compromise between the two. And for some bizarre reason, the aftermarket often did better than the OEM's; my Honda 750 bike with a Supertrapp exhaust made much better power than the stock pipe, yet was also relatively quiet (that was the exhaust where you could add or delete some discs to tune the exhaust). And yes, the vacuum line rats nest of some of those smog engines was enough to drive us nuts! One little crack in those rubber lines would make the car run terribly! I vividly remember taking polaroid pictures of the top of my engine, pulling off the Autolite carb and replacing it with a pre-smog Holley, plugging up all those little holes, and running it like that until the next emissions inspection when I'd reverse the whole shebang! Ahhh, the good old days!
Damn bro you are smart af!! I’ve been following you for a couple years now and bro I have learned a lot from you
Great videos! Thank you so much from a fellow engineer. Sometimes it's difficult to see concepts of theory applied, but you made a brilliant job ;)
Great video and very easy to follow explanation. I work in automotive parts and it is constantly preached by many that "you have to have plenty of back pressure". No one knows why but they are certain it's true. Thank you for debunking this ancient rumor.
Thanks for clearing this up. I have argued with people for years about this but now I can just tell them to watch your video. Great explanation man
I didn't think that exhausts had to manage pressure to that sort of precision! Details like these are interesting to see manufacturers get into. Thanks EE!
What a lecture! you have taught me so much, absolutely brilliant. THANK YOU
He lost me at hello
@James D 😶😶
It’s not that hard of a concept
"and welcome"
It was just too much for the poor guy to handle.
He must have been on one of those "three cups of coffee" days.
Did he say hello? I noticed some pictures. Then something about "scavengers"
You lost all credibility at this comment
As always you deliver the most interesting and understandable discussion. Thanks for sharing your extensive knowledge.
Excellent video thank you for this one! So many people get this wrong and it's really hard to try to explain it to them without a good visual aid to go with it and you made it really simple to wrap your head around.
This is why great aftermarket exhaust systems and great tuning go hand in hand. Yes they are expensive due to all the R&D that must go into the correct design specifications.
I have been applying this for years and it is nothing short of incredible how much torque can be found by building a proper exhaust system. not only length and diameter but collector and muffler design.
I think the myth comes largely from very old cars, with extremely inefficient high back pressure exhaust systems -like original VW Beetles -if you fitted a free-flow straight-through exhaust to them, it would make such a dramatic change to flow / air:fuel ratio, that if you didn't change the carburettor settings at the same time, they often wouldn't start or would run very badly, historically motor manufacturers would tell mechanics and anybody that asked, that this is because you "needed back pressure" because they didn't want to encourage people to modify their engines, as they had other concerns like reliability, longevity and low noise.
I think it more comes from people putting oversized diameter exhaust on their vehicle and losing power/torque because the exhaust velocity has slowed down too much. They don't realize there is a difference between free-flowing and oversized.
Their carburetor was set up fora high back pressure exhaust and they put on a low back pressure exhaust and now it don’t run the same. That’s when they say they “ need back pressure”
that's what I thought when I had a rusty hole in the exhaust but my emissions were bad untill I fixed it. And it's not an old car.
Loss of power due to oversized piping is a bit more complex
If the working routine of the engine is not modified, it will keep on kicking the same quantity of gas out for a given load, no matter what pipe size is used
The loss of power is not due to the fact it looses velocity on getting out of the engine but on the pressure in the cylinders
A bigger pipe allows more gas out so the cylinders will be emptied easier but If the cylinders feeding/emptying scheme is not modified, some of the mix supposed to ignite wil slip through the exhaust system before it is consumed, which turns out to leave less mix in the cylinders, giving that loss of power
It's pretty simple
Bigger exhaust implies better ignition timing
@@sethmanukula176 Yeah exhaust valves usually open before BDC
Very well said. Its a pet peeve of mine about back pressure. Its as if piston fighter aircraft arent a thing. No backpressure and scavenging is done via Bernoulli from airflow passing over the end of the pipe.
This makes sense and fills in the gap when thinking about Motordyne's shockwave exhaust. The gradual expansion from 2.5" to 3" is sending back that negative pressure from constantly stepping up helping the exhaust gases from the other cylinders
As much as I THOUGHTI knew at least about the basics of the 4 cycle combustion process I had no idea about how the positive flow backwards to the exhaust valve effected the next stroke...this is DAMN good stuff you've done it again! Happy New year BTW my man!
Great video Jason! Happy new year from Australia!
Happy New Year!
I have a friend who doesn't pass gas very often. After careful thought we figured he didn't stop talking long enough to build up any back pressure. Continued good work with your videos.
Excellent video. Amazingly no one spoke about L/D ratio, also known as slenderness ratio.
Vent at the headers as god intended.
Nice to know your god created the internal combustion engine... Carry on
Zoomies😍
mcf3778 I think/hope it was a joke (ish)
No!!
Yeah it was a terrible joke and some people failed to see it.
I think people used the term "back pressure" without fully understanding what it is. Thanks for clearing that up.
Learned the principles of exhaust tuning via the reflective and transmitted waves in vibroacoustics and have always jut shook my head when people talk about back pressure and why its needed in an engine (aka air pump).
Very good video. Would you try please to explain better about the sweet spot, where we get the optimum flow and equilibrium between back pressure, inertia scavenging and velocity. How can we calculate it.
I thought that a bit of back pressure was good from what I've heard from people but I guess not. Thanks for making this video, this clears up a lot!
Many years ago, engines ran a fairly large amount of overlap (intake valve opened well before the exhaust valve closed) in order to scavenge all the old burned fuel out, with a large amount of muffler backpressure. If you ran straight pipes with no backpressure, the incoming (cold) air/fuel mixture would flow out the (hot) exhaust valve, and could cause the exhaust valve to warp. As muffler design has improved, we can get lower backpressure with similar noise dampening, so I believe the overlap is now shorter. So maybe valve warp would not be a problem anymore, but I don't know.
David Vizard wrote about this (World Horsepower Guru). He commented on some brilliant testing that drew the wrong conclusion. The test with more backpressure did gain power because the muffler designs were different and changed (inverted or moved) the pressure wave tuning point at the end of the pipe. It happened that the more restrictive muffler had the better resonance tuning. More or less what you say here, but it should have been more widespread knowledge
Have you heard of "pressure wave termination boxes"? It's a trick used to simulate having open headers (no exhaust) while actually having a full system
The inverse trick exists too. Headers designed for use with cat converters immediately after them (but in use on a non-emission car) can have a temporary (and hopefully smooth) decrease in pipe size to simulate the wave reversal characteristics of a cat converter.
Wave tuning is cool. I play with it on Engine Analyzer. I've seen (simulated) volumetric efficiency of 112% at times
Great work mate. Another awesome video. I learnt a lot. Cheers.
Excellent video, I finally understood how all these phenomena work, thanks man
Jason, keep up the good videos. Loved this one! Happy New Year from Down east.
Scott Stonefield I’ve been watching this dude for 4 years and just today learned his name is Jason...
I’m so glad you made this, too many people think back pressure is a must to have on a car!!! I’ve been arguing this for years!!!
Haha yup, I don't think I could find a better example of an engine designed with this goal in mind, than the Porsche 918's. Reverse-flow heads, and the entire exhaust system is like 6 or 7 inches long
Talk to the racers if u think back pressure is bad.
Its about the pressure wave, a completely open exhaust won’t scavenge and mid range torque is lost
I always like your videos! They are very informative! Thank you!
This video just helped me understand how I need to build the exhaust on my Truck. Thank you!
The Dislikes are the people that said the car exhaust needs BackPressure.
Miguel Ruiz the only type of engines that needs back pressure are 2-strokes I think that’s where they got that from
@@zippyoya typically the flow should be balanced. If your exhaust is sucking raw fuel out of the cylinder before the valve closes you might consider changing the flow of the exhaust. Valve timing sometimes overlap incorrectly. Also the expansion chamber of the 2 stroke doesn't create back pressure.
I disconnected my cat from my old 90 4runner once and it felt 10-20% slower.
r2dxhate that makes no sense a high flow exhaust wouldn’t change that much you might get a gain of like 1.5 to 3 horse power not much
@@zippyoya I'm not talking about a hp gain, I said my 4runner got slower. Someone suggest my cat might be clogged, so I disconnected my bolt-on cat to see if it ran better with no exhaust at all besides headers, and it was way slower instead. I'm not saying that proves engines need back pressure, but for some reason it wasn't running as good when it was allowed to breath better.
Decades ago when I was helping out a SCCA team, our engine guy made 2 sets of headers. One set was equal length and rather short to maximize peak output at higher RPM. For some tracks needing a bit more midrange torque he had another set with a short and long tube set mixed. This was a better compromise than all equal longer tubes that gave more low torque, but really dropped off the high. Half of engine building is exhaust design. One engine guy I knew even made internally tapered steps hidden inside the constant diameter OD of the header pipe ( to hide the steps) in order to better control the back wave to his desired flow characteristic. Interesting combination of fluid dynamics and acoustic pressure waves in exhaust systems...
Jennifer WhiteWolf Multiple EP national champ Joe Cogbill had engines for his 96Rock Speedster specific for fast and slow tracks. IIRC the fast track engine had a 1.75” dia. exhaust and put out 172 HP. The slow track motor utilized an exhaust of 1.625” dia. exhaust and put out a max of 158 horses but more in the lower rpm.
jockellis; do you race too? You comment about 96rock makes me think you're from the Atlanta area.
Ornery Hermit Well, I went to the Skip Barber 3-Day school at Roebling Road and raced Karts on ovals but no other wheel to wheel racing. But if I can ever get my 914 project car finished I want to go hill climbing. I interviewed Joe for a story for VW & Porsche Magazine but could never figure how to save it to my Radio Shack Model 4 and it kept disappearing.
Wow. Talk about a small world. My first racing school was also with Skip Barber at Roebling. We ran Formula Dodge open wheelers (no wings). Then I did the SCCA school in a rented Miata at VIR. Been racing spec miata and Spec Racer Ford's since then. Will actually be at Roebling Road again later this month for a SCCA event.
Ornery Hermit How fast could the FDodges go around that last turn onto she straight? Did Bruce McInnis run the school?
Fascinating, and impeccably communicated as always!
I Love these videos. there are so many hundreds of Nuances to car design that i learn about each time.
this makes me scared of making any modification to my car exhaust now
Just use parts engineered by well known manufacturers like Borla
or just use what he just said and if you use bigger diameter piping, tune it correctly. most cars come stock with 2-2.5" exhaust piping. you are gonna have some back pressure at the header collector, downpipe/cat. use the available bp to balance it out and a tune to dial it in.
It's just pressure vrs flow
you can't really damage anything with the parts that you can mount on a road car. But something similar to the stock exhaust or well-engineered aftermarket is better for sure.
@@MrHaggyy like a Flowmaster hush power 2 muffler and two or two and a half inch pipe to the rear bumper?? Or is this too free flowing?? It's a V.6 tiburon.
Back pressure is helpful in a 2 stroke engine, hence “tuned pipes”
kinda... how an expansion chamber (tuned pipe) works in stages. when the pressure is moving back to the piston from the exhaust it's in the compression/intake stage it's good (helpful). any pressure that moves back during the power/exhaust stage (back-pressure) is bad. the reason the pipe is so fat in the middle is to reduce back-pressure in the power/exhaust stage.
thats why 2 stroke enduros have those resonators.
@@gatorage850
A clearer explanation is that a tuned pipe is designed to allow sound waves to reverberate back to the exhaust port when the air/fuel mix is compressing.
This allows a sort of pressurized charging by pushing the air/fuel mix that would otherwise be wasted back into the combustion chamber.
Tuned pipes are only effective at a range of RPMs that time the reverberation of the sound waves with the compression of the air/fuel mix.
The fat part of a tuned pipe is at a distance from the exhaust port mathematically calculated by the exhaust gasses moving through the given diameter of the exhaust pipe at the speed of sound, usually 1/3 wave.
This is why a power band fades away as the exhaust becomes overheated as well.
@@kaisersose5549 I was trying to keep it short/simple and just showing the pressure on. mostly the end result of the wave affecting gasses near the piston. not trying to explain the whole wave process for how technical and confusing it could be for someone new to understand/picture clearly or want to read.
Once again - brilliant , so well done
As an old two stroke bike racer the effect of correct exhaust tuning is something I am very familiar with. One small addition and that is that exhaust pressure waves do not necessarily move at the speed of sound. That speed can vary slightly depending on exhaust temperature. Also perhaps should have emphasized correct lengths of the different runners so pulses are not fighting each other.
Happy New Year.
Best wishes.
Happy New Year everyone!! 2017 was truly an amazing year here at EE, and I just want to say thank you all so much for continuing to watch, share, comment, (and even criticize occasionally, I deserve it haha), and most importantly maintaining your curiosity. Personally I think education is one of the most important things in order for people to progress and move forward in a positive manner, and I'm happy you've all joined along with me on this adventure. Don't stop learning, whether it's from your teachers & professors, friends, family, or even some nerdy kid on the internet who's greying far too early. Let's have a great 2018!!!
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Engineering Explained exaust dynamics is a really complicated problem. 2 stroke engines needs back pressure tho.
Does any car have variable length exhaust piping? from your explanation the best performance would come from "decent" non restrictive diameter piping with variable length "wide-chamber" to control low pressure wave timing. Is there anything like this on the market? Thanks, and keep up with your great videos!
Am I correct that in some cases, a more restrictive header might be used to increase lower end power/torque, but hurt the over all maximum power?
Engineering Explained You're great man, keep it up.
i couldn't agree more with you comment on the education. (p.s. "you" are my favorite professor! )
The way it was explained to me (by aeronautical engineering school) was back pressure was needed to help clear the space between the piston and top of the cylinder when the piston was at the top of the stroke and both the intake valve and exhaust valve was open. The air/fuel mixture would push out the remaining exhaust whilst the back pressure would restrict the amount of air/fuel mixture from entering the exhaust pipe. Not enough pressure could cause ignition in your exhaust pipe. However the engines we worked on were old VW boxer engines which surprisingly made pretty good aeroplane engines
Wanted info on back pressure, knew to look for EE for a good explanation!
I have been trying to teach this to people for decades. They don’t learn. Please everybody, spread the word!
Michael DeJong seriously. Ive been trying to get this misconception out of peoples heads for years now.
The physics involved here are fascinating and is just a single area of improvement with engineering. It's sad to think of how all the really cool physics involved in ICEs may be displaced with electric and software. There's a lot of skills and knowledge that is potentially at risk. (Said by a father who will teach his son how to overhaul a small engine as soon has he is old enough to use a wrench.) Happy New Year!
Sounds like a fun activity - for you. Unfortunately, it is a skill that is becoming less and less valuable each day and he might not even have the opportunity to use it much if our roads go the way of autonomously driven electric cars when he's an adult. I think your fears are correct. Maybe learning to make his own PCBs to hack a Tesla would be more useful . . . I grew up in the '70s & '80s and I remember when dad got an electric weed-eater, then an electric leaf-blower and slowly, our garage went from lots of small ICEs to extension cord racks.
Less so than ICEs disappearing, I fear loosing a more accessible and tangible technology to learn. A young child getting hooked on ICEs might later realize them as a gateway to Physics, ME, or AeroE (or environmental conservation.) Who knows their trajectory. Modern electronics are pretty highly integrated, so mostly serial protocols, software, data sheets and integration. Early on it's more about creating experiences, especially sensory, and the ability to adapt. I spent a lot of time at university and every time a topic was completely dropped the students suffered. The argument was always the same... "computers can do this for them, they will not need this in 10 years."
BTW: You guys were way ahead of everyone else. Today, I only know one person with an electric mower and two (high income) people with electric cars. Might be regional thing.
Have a good one!
I don't understand older generations sometimes, look at car engine progression over the last 20-30yrs gone from a mechanically operated engine that was time consuming to diagnose or fix. now to having inputs that a very impressive that are processed at the speed of light, even looking at fuel trims can give easy idea of where to diagnose the problem, it was only easier back the ole days cause u did'nt have to worry about catalyict convertors or evap codes u could vent the engine crankcase straight into the atomsphere( a no no in todays world) and the fact its easier for the modern joe to keep his car serviced, or u gotta do change the oil,no more replacing contacts on dizzy.
if u know how to read a relay diagram u know to diagnose problems for electrical theres alot of good channels out there. engine still use the same princepal air/fuel compression spark, just different way to operate.
This is the best explanation of exhaust pressure I've heard, thank you
this is a fantastic explanation. whiteboard visuals really help
It would be great to talk about turbos and whether or not all these effects does still occur behind it. :)
Nounours2627 you want that pressure wave to be as consistent as possible drawing maximum air out of the engine as possible. Ie maximum velocity with minimal resistance to keep the turbo spooled higher.
Great video Jason, and really interesting topic! One question, did you learn all of this knowledge in your degree, or did you have to research it for this video, because it seems like they are some really specific knowledge and phenomena to have learned at school.
coscorrodrift I believe he learned some of the basics through classes-thermodynamics, design, etc and then did self study outside the curriculum
Most of this is from online research - there were a few well researched papers and articles I found on the subject for bits and pieces. As is generally the case, there's a lot of good (and bad) information floating around on the internet, just needs to be sorted down to the facts. That's my goal! As far as my degree, I just did a bunch of challenging math problems for four years haha. Not a huge amount of practical knowledge, but definitely problem solving skills.
Great video, this is for non-turbocharged vehicles though, with a turbocharged vehicle you just want the highest flowing exhaust after the turbo as possible. All the scavenging etc happens in the headers before the turbo
I think a turbo dampens out some of the pulsations that are important in a non turbo system making post-turbo more about big cross section and less about "scavenging"
Great lectureo bro, keep em coming!
Great explanation. I'm learning the older I get, the more I trust OE engineering, and I just leave my vehicles alone. Big automakers probably have more R&D money than a backyard fabbing company. Take care! Awesome channel.
+ Bushcraft North of 60 : Well, it's not so much that they do more R&D per se... It's more that as you age, you realize that daily driver vehicle functionality and reliability are far more important than a little extra horsepower or torque.
Typically, when a person starts "screwing" with any engine outside of the OEM settings, you will find more power, IF and ONLY IF you have a clue what you are doing. That said, typically the engine becomes less reliable and more expensive to operate. It's really just common sense. (Sadly, something that many folks lack.)
That said, there are always some exceptions to the rule. For example, most modern emissions controls are literally "choking" the longevity, economy, and power outta the modern ICE's, both gas and diesel. That too is a proven fact.
You'd be amazed how many people I've come across that think they are smarter than a department of German engineers.
I quickly swapped my Urethane Transmission Mount back to a stock mount after being vibrated to death in my LT1 Pontiac Formula, the OEM people really do their homework/testing about components & conditions.
After a HiPo build they recommend running the pipes off the headers right out the side, wind up the engine until white hot, cut pipes where they change to red and you have a race car exhaust.
But, as TurboDiesel said, a daily driver is usually better off without screwing with it. The tuned exhaust (and I don't mean "tuner exhaust" on ricer cars) is tuned for a specific purpose - whether it's drag racing, circle track, or whatever, but it's not ideal for daily driving - unless you tend to drive stoplight to stoplight in 12.0 seconds or less.
I never believed in backpressure, but I wanted to watch this anyway. Care to elaborate on what methods manufacturers use for turbo applications? It's going to act as a restriction for sure but are there any tricks manufacturers use to mitigate this?
Generally for turbocharged applications, you simply want low restriction after the turbo, because you're no longer going to gain the benefits of scavenging from exhaust pulses. Leading up to the turbo, you want to keep routing short, and hot, so that little energy is lost from the exhaust valve to the exhaust turbine.
Engineering Explained
To me that sounds like a short and fat turbo manifold leading into the turbine side of the turbo with a high flow cat right after it, and the absolute lowest possible restriction muffler after the cat to keep noise humanly acceptable. I am simply not psychopathic enough to needlessly pollute. Droning exhaust notes get old real quick.
Thankyou Robert for taking the time to be in the video, I am sorry for any disrespect. I have caused. I have caused. I hope you are well wherever you are right now. Thankyou.
Late to finding this video, but glad I did because it verifies info I've sat on for many years. I could never figure out why people promoted back pressure or built it into their factory vehicles. My guess is more back pressure resulted in less evacuated gasses giving lower emission readings to meet regulations.
I found this video very interesting because about 25 years ago I was getting into R/C Airplanes. The fellow teaching me had an advanced Pattern competition plane that used a "tuned" exhaust pipe. Not understanding what this did for the plane I decided to research it. In my research I stumbled across an article about Reno Air Racing Midget Pylon racing planes. If I remember correctly all planes were restricted to a certain, and rather minimal, engine size. One of the very things the racing teams did was to tune their exhaust pipes to maximize exhaust gas scavenging and increase the intake of air/fuel creating more power, just as this video explains. Ever since I read the article, one of which made very good sense, I could never wrap my head around the back pressure theory.
nicely explained, thank you very much.
one thing that puzzles me about the scavenging:
how can you tune the desired pressure effects with fixed length exhaust parts, when most of the other parameters like exhaust pressure, velocity and timing between cylinders must vary significantly depending on rpm?
Generally you're tuning for a specific RPM window - for example in racing when you know RPM will remain high, you tune for peak torque at higher RPM (and thus also peak power). For passenger cars it's difficult to do, because a wider torque range is more favorable (turbochargers can generally accomplish this well).
Engineering Explained
My field is biology based, so I am not far above caveman level on this. When you add boost, by supercharger (wider RPM) or turbocharger (narrower band) you increase flow through the exhaust system. Should you expect to leave a stock exhaust and catalyst system stay in line without blowing the stock converter? I am thinking about the Edelbrock SC CARB system for the MX-5 ND (and aftermarket CARB turbo systems) that require the dual catalyst stock exhaust.
Great video thanks for the education!
Turbo and supercharger system next?
Removing back pressure on a diesel (emissions delete/larger diameter pipe) makes a huge difference in the amount of power an engine can safely produce. The better flow enables you to tune for a lot more power while keeping EGT at safe levels. If you attempted the same power tune with factory exhaust the turbo(s) would fail.
BrianNC81 Quite an antisocial adjustment though, as the dpf is designed to reduce small dust particles from your exhaust gasses by up to 90%. These days almost everyone has a member of their immediate family that has died due to cancer; I just don't see why anyone would decide delete the dpf. And even be proud of it...
Niels Onderbeke I'm glad my truck was never equipped in the first place with DPF due to it's age. Better reliability, mpg, and power. A diesel without a DPF should not smoke if tuned well but there are idiots out there that dump a lot more fuel than needed to put out more smoke on purpose. With an optimal tune it should be fairly clean without DPF.
Not even close.There is a reason the dpf exists or all diesels would be still be made the way you claim.Its called progress......
Its called government regulation.
It's my impression there are important acoustic effects after the collector, and the length of the exhaust pipe from the collector to the "resonator" is important, and removing the resonator but maintaining the total exhaust length can negatively impact performance.
I have to think through this negative pressure thing a little.
You explain the back pressure question I've had for years. Thank you.
I had a 69 Dodge dart Swinger with a 340 and later I saw on another Dodge police interceptor, immediately after the exhaust manifold there was a 2" pipe from 18"-24-" then expanded to 2 1/4" after.
One question I had when you were explaining the scavenging effect was what about the valve overlap? Older v8's typically had about 15-20 degrees crank rotation of valve overlap.
How would I calculate the correct size and tube length? Or as that just trail and error?
My car has a 2-stroke sooo, my cars exhaust needs reflective sound waves :D
but yeah planing to put in a 4 stroke and then that dose not matter anymore and i have to remove the components that are tuned to the 2 Stroke. ^-^"
your videos help understanding what i have to consider with the conversion - keep it up your a big help :)
kind regards Lara
back pressure will severely harm the performance of a 2-stroke here again you are confusing back pressure with the reflective sound waves as it works the same way in a two stroke.... reflective sound waves are much more critical for the performance of a two-stroke to keep the intake from escaping the exhaust port. these are not my words but the words of Pop Yoshimura the greatest tuner of all 2-stroke engines there ever was and the inventor and designer of Honda's first two stroke engine
@@donniebaker5984 edited it to be correct :)
Reminds me of many debates on dsm tuners lol. Great community and there def where guys who understood the concept of exhaust pressure and velocity and how it changes throughout the rpm band.
Your explanation just gave you a subscribe!
Thanks for the laugh! I did a test on this on my car during the Spring of 1990. With no back pressure, the car had no bottom end power, meaning power picked up around 3500 RPM. But with back pressure the car could do burnouts. This car didn't have turbo. This was before EFI. A class to take is fluid mechanics in a pipe. Here again, no two engineers have the same solution.
Thank you, what you have are a bunch of people trying to eliminate the word back pressure when if you have to much pressure in the exhaust system you kill exhaust gas velocity and it you have to little pressure you kill exhaust gas velocity. It is all about finding the right sized pipe for the highest exhaust gas velocity.
Where all the misinformation and confusion comes in is an exhaust system is not designed with back pressure, an exhaust system is designed by maximizing exhaust gas velocity. John Lingenfelter built 600 horse power Corvettes and Borla worked with him on the exhaust systems, John Lingenfelter used 2 1/2 inch exhaust systems because that is what provided the best exhaust gas velocity to make the most power, as Borla says if a bigger pipe would have made John Lingenfelter go faster he would have used it.
Does my butt have back pressure when I fart?
Yes, the sphincter has a smaller diameter than the colon. This could be the reason for two toots sometimes.
In your case yes. It causes brain damage.
No. That's scavenging.
Are you wearing spandex or cotton?
If the smell gets passed your underwear and jeans to people's noses than you don't have enough back pressure !
This was an awesome explaination!
You get a shock wave with a p0/p1 ratio at about .52. that's certainly something you want to avoid. So the lesson is try to cool that exhaust as much as possible before it hits atmosphere. Pressure drop can be modulated by expanding the exhaust size and channeling it though passages to even out and cancel sound waves. P0 = P1 + .5pV*V
So all those coffee can mufflers on the rice burners really do suck? So fitting!
They should teach this in school
I learned this stuff from a book written in the 1960s.
They do, in college
I learned this at UTI, but I think I'm the only one who listened.
They do at least the basic principles in AP Physics at least they did when I was in HighSchool
They do once you get passed the 4th grade. Be patient.
very nicely explained. good info.
Love your channel, Jason! I might disagree on this. Engine with no back pressure run really weak. I tried this on moped😆
Lol you demolished the backpressure argument in 1 minute 58 seconds 😅
He did not demolish anything, to much back pressure in an exhaust system and exhaust gas velocity is killed, to little back pressure in an exhaust system and velocity is killed, all these videos do is play semantics trying to say back pressure is a myth yet all properly designed exhaust systems will have back pressure. It is about exhaust gas velocity. Borla worked with John Lingenfelter and he built 600 horse power corvettes using 2 1/2 inch exhaust systems because that is what gave him the maximum exhaust gas velocity if a bigger exhaust pipe would have made Lingenfelter go faster he would have used it but a bigger exhaust pipe removed more restriction i.e. back pressure and killed the exhaust gas velocity.
A 2 inch exhaust will only flow so much volume, a 2 1/2 exhaust will flow more volume than a 2 inch system and a 3 inch exhaust system will flow more volume than either a 2 inch or 2 1/2 inch exhaust system. What you are looking for is exhaust gas velocity if the 2 inch is to restrictive you kill exhaust gas velocity what is restriction, it is back pressure. If the 3 inch exhaust is to free flowing it kills exhaust gas velocity because it does not have enough back pressure. The 2 1/2 inch exhaust in this case has less restriction than the 2 inch system and has more restriction than the 3 inch system yet the 2 1/2 inch exhaust system has the highest exhaust gas velocity.
Having said this what you have to do is design the entire exhaust system with the optimal size pipes to get the maximum exhaust gas velocity so it takes proper design to get maximum results, which is why Borla is the leader in aftermarket exhaust systems and they have won more races than all other aftermarket exhaust manufactures combined.
All these videos are doing is using mental gymnastics trying to eliminate the word back pressure.
Excellent video! You've answered many of my questions except one. How do I figure out what is the correct tubing length and diameter if I was to design an exhaust system so that it makes power instead of losing power?
No exhaust! JK
i think thats the hardest part...
i'm pretty curious too
@@billbergen9169 No exhaust usually is not the answer. There is no "tuning, no scavenging effect.
This is so old, anyone figure it out how to calculate those?
2.5" for motors up to 2L
3" between 2L & 4L
4" for 4L to 6L
Dual pipes on the V motors & use a H pipe for the low end and better sound.
That's really cool I never really took into consideration the pressure waves coming back. I guess the length of each tube going to the collector has to be rather precisely optimized to account for this. I guess things can get even more complicated when you start introducing turbos.
Turbo complicate matters, but they do work to simplify them a bit as well.
The turbo itself can help pull the exhaust once it gets going, but then it needs more pipe once it gets going...
I think most of my successful buddies had normal sized pipe before the turbo and a little larger than optimal for NA afterwards, pretty much any piping after the turbo seemed to hold in heat, once the turbo spooled up the air was going away as long as there weren't any serious restrictions, the exhaust pulsing vs the length of the total exhaust wasn't a factor. The turbo itself broke up those pulses.
So cool. I didn't know there was this much to simple exhaust tube.
I'm a little suprised that anyone has even heard of this old piece of advice. Doesn't have anything to do with scavanging. Dates back to when vehicles were still carbureted. If you significantly changed a cars' breathing capabilities, you screwed up the carb tuning, and there was no computer to mod the A/F ratios. Every kid in high school would slap on open-element air cleaner and headers with straight pipes, but no one would bother to dig into the carb and change the jets and rods. The result would be that it would start eating gas and wouldn't really idle right, and you'd be throwing HP right out the tailpipe.
Stock 289 High Performance Mustang from Ford, 271 HP. Shelby Modified High Performance Mustang 306 HP?
Why not? The pressure waves make sense as well.
Also some eary fuel injection motors computers are too simple and dont know how to do anything but stock
It's the same concept be it ecm or carb. If you change something to the car, motor intake exhaust etc, you have to tell the computer you made those changes otherwise it will keep doing what it was programmed too. Same with carb if you dont adjust or change the jets it will keep doing the same thing. Causing the idle issues, spitting unburned fuel air out the back, and other things
Shouldn't fueling then be retuned after lowering back pressure (with straight piping). I've read (at least on carbed motorcycles) that any considerable changes with back pressure (straight piping) always have to be accommodated with fueling retunes otherwise the engine will run too lean or too rich (because it was tuned with back pressure from the stock exhaust in mind in the first place). Am I wrong to think this?
my mustang needed back pressure because thats how ford designed it without it i lost a lot of torque i could feel i lost power in the gas pedal high flow mufflers and huge h pipe yeah my motor revved higher easier but when it came down to putting power on the ground hell no....explain with diagrams and whiteboards all you want i bolted the part on and felt the difference so you cant say all engines dont need back pressure new variable cam engines are being designed to use the exhaust gases to reduce displacement so how does this apply to that
I've heard very similar things, at least in the case of bikes. I know with fuel injected bikes getting a free flowing exhaust will do very little without a fueling retune, maybe that's what your thinking about? IDK I'm just some guy on the internet
Xantho - Correct. Matching intake with exhaust is the whole idea.
In the example, we do have back pressure. That creates the velocity to generate the vacuum wave at the end of the exhaust valve opening? Here again, balance is critical.
Theonlylee1984 your forgetting the fact that without any upgrades to require more exhaust flow you won’t get any power gain from it
If someone buts a blower and cam on their mustang they will prob want to open up the exhaust
But with stock motor and bigger exhaust you do loose torque and power
An excellent, no fuss, no look-at-me, explanation. Well done.
This is like a thin film antireflection coating for an optic. Amazing how waves apply to pretty much everything.